It is well known that amines such as hexamethylene diamine can be produced by the catalytic hydrogenation of nitriles such as adiponitrile in the presence of Raney Nickel catalysts.
One such process is described in U.S. Pat. No. 3,821,305, in which hydrogenation is conducted in liquid phase at pressures of from 20-50 atmospheres and temperatures of 60.degree.-100.degree. C. in the presence of finely divided Raney Nickel catalyst and an inorganic base. Hydrogen and adiponitrile are fed into a liquid reaction medium consisting of hexamethylene diamine, water, the inorganic base, and the catalyst, in which medium the content of base is maintained in the range of 0.2-12 moles per kilogram of catalyst, while the content of water is maintained in the range of 2-130 moles per mole of the base.
The process discharge stream in the above described process contains both Raney catalyst and the product hexamethylene diamine, from which it is desirable to recover substantially pure hexamethylene diamine by distillation, and to recycle the Raney Nickel catalyst.
Before distillation of the process discharge stream, the stream is ordinarily fed to a decanter or container from which the crude hexamethylene diamine is removed as an upper layer and a catalyst slurry is removed as the lower layer. This catalyst slurry is normally washed so as to remove foreign materials including aluminates, carbonates and caustic. This washing, through recycling of the catalyst slurry, increases the settling rate of the catalyst in the decanter.
However, separation in the decanter has been found to be inefficient due to a high content of fines in the upper (product) layer.
Any method whereby the setting characteristics of the product stream could be substantially improved would constitute a significant advance in the art and in an object of this invention.